My understanding of the flow of matter is - that the wife was a prosecution witness.
She was in court to testify that Thuo was fine when he left for the Pub - obviously implying that someone at the pub poisoned the guy.
The story of how she related with him is an affront thrown her way by the defence counsel to muddy the waters and create doubt to benefit his client(s)
Isuni yilu yi maa me muyo - ni Mbisuu